Mine is 3-pronged:

btrfs + snapper takes care of most level-1 situations, and I take a snapshot of every /root change, plus one nightly /home snapshot. but it’s pretty demanding on disk space, and doesn’t handle drive failure; so I also do

restic + USB drive, which I can cram way more snapshots onto, so I keep a couple of weeks of daily snapshots, one monthly snapshot for a year, and one snapshot per year, going back several years. I currently have snapshots from my past 3 computers on one giant drive. However, these drives can also fail, and won’t protect me from burglary or house fire, so I also do

restic + BackBlaze. I just take a nightly snapshot for every computer and VM I manage. My monthly B2 bill is around $10. The VMs don’t change much, and I only snapshot data and config directories (only stuff I can’t spin up fairly quickly in a container, or via a simple install command), so most of the charge comes from a couple of decades of amateur digital photography, and an archive of all our digital music (because I’ll be damned if I’m going to spend weeks re-digitizing all those CDs).

The only “restore entire system b/c of screwing up the OS” is #1. I could - and probably should, make a whole disk snapshot to a backup drive via #2, but I’m waiting until bcachefs is more mature, then I’ll migrate to that, for the interesting replication options it allows which would make real-time disk replication to slow USB drives practical; I’d only need to snapshot /efi after kernel upgrades, and if I had that set up and a spare NVME on hand, I could probably be back up and running within a half hour.